The present invention relates generally to the electronic test apparatus art, and more particularly is concerned with the testing of single and multiple semiconductor junctions for the purpose of determining their operating condition.
The semiconductor tester disclosed and claimed in U.S. Pat. No. 3,973,198, titled "In-Circuit Semiconductor Tester" and having the same inventor as that of the present application, was a significant advance in the art at the time of its invention, because it was capable of accurately and completely testing a single semiconductor junction while the junction was still connected in circuit, even low impedance circuits. The apparatus of the '198 patent, the subject matter of which is hereby incorporated by reference, has been found experimentally to operate very well and has fulfilled the expectations of its inventor. The apparatus has been found to have some operating limitations, however. For instance, in some circumstances, it is desirable to test multiple junctions, such as from emitter to collector of a single transistor, or to test cascaded junctions. The U.S. Pat. No. 3,973,198 apparatus is not capable of completely testing multiple or cascaded junctions due to their relatively high AC impedance. The visual patterns produced in such a situation are often difficult to interpret, and may in some cases be misleading.
Additionally, certain types of transistors, such as power transistors, as well as multiple and cascaded junctions, require a higher firing voltage than is currently available in the U.S. Pat. No. 3,973,198 apparatus, and hence the junctions in those transistors cannot be tested.
Further, it has been found that the U.S. Pat. No. 3,973,198 apparatus is in operation often difficult to match with available oscilloscopes, leading to an impairment in usefulness of the tester because of the increased difficulty in interpreting the resulting visual patterns or trace. In some cases, due to insufficient horizontal gain, a particular oscilloscope cannot even be used. Furthermore, the use of an oscilloscope with the U.S. Pat. No. 3,973,198 apparatus has proven to be an inefficient use of the scope, and the U.S. Pat. No. 3,973,198 apparatus hence sometimes is not used in situations where it might otherwise be beneficial.
Accordingly, it is a general object of the present invention to provide an improved semiconductor tester which overcomes the disadvantages of the prior art noted above.
It is another object of the present invention to provide such a tester which is capable of accurately determining the operating condition of both single and multiple semiconductor junctions.
It is an additional object of the present invention to provide such as tester which is capable of accurately and completely testing single and multiple semiconductor junctions without harming either the junctions or the circuits in which they are connected.
It is a further object of the present invention to provide such a tester which is capable of testing semiconductor junctions both in and out of circuit.
It is an additional object of the present invention to provide such a tester which is capable of simultaneously showing the forward and reverse characteristics of the junction or junctions under test.
It is yet another object of the present invention to provide such a tester which is capable of providing a sufficient magnitude of voltage to fire substantially all semiconductor junctions, as well as multiple junctions, at a limited current level which is sufficiently low to prevent harm to the semiconductor.
It is a further object of the present invention to provide such a tester which includes an oscilloscope and a testing circuit in a single, portable apparatus.
It is an additional object of the present invention to provide such a tester which includes a testing circuit producing output signals which have a preselected voltage level adapted for use in the integral oscilloscope.